The reported association of mitral valve prolapse with autonomic dysfunction and neuroendocrine abnormalities is derived from studies of patients selected because of symptoms or specifically referred for investigation. To determine whether such associations occur in nonreferred and unselected women with mitral valve prolapse, we measured blood pressure, heart rate, and norepinephrine response to standing in 13 volunteers with mitral valve prolapse and in 11 control subjects. Platelet alpha-adrenergic receptor quantity and affinity on standing also were determined in all persons. No significant differences were found between the groups in any of these measurements. Although small subsets of women with mitral valve prolapse may indeed have associated neuroendocrine epiphenomena and autonomic dysfunction, it is probably incorrect to generalize these findings to the vast spectrum of those with mitral valve prolapse.